1. Field of the Invention
The present invention relates to an image processing apparatus, an inkjet printing apparatus and printing method, and more particularly, to technology that uses an image quality improving liquid, which substantially does not include color material, to suppress bronzing and interference color in a printed image, while improving glossiness and color reproduction.
2. Description of the Related Art
A technology that overcoats a print medium with yellow ink, as described in Japanese Patent Publication No. 4066338, is known as a technology that suppresses this type of bronzing. More specifically, after printing an image onto a print medium using cyan, magenta, and yellow ink, yellow ink, which produces little bronzing, is applied on the printed image with a print duty of 10% or less. This enables a reduction of bronzing for cyan hues in particular.
However, in some cases, the method disclosed in Japanese Patent Publication No. 4066338 is difficult to implement for images that use colors of many hues. More specifically, using yellow ink may cause problems that impair image quality due to changes in tint, such as lowering the saturation of certain hues and disrupting the gray balance. Also, with the method disclosed in Japanese Patent Publication No. 4066338, the phenomenon of color change in reflected light produced by thin-film interference (hereinafter also designated interference color) is not resolved.
A known technology for resolving the such problems involves printing by using ink containing ordinary color material together with clear ink which substantially does not contain color material and to which a water soluble resin that dissolve in ink is added, or ink called image quality improving liquid. This provides a certain effect of suppressing bronzing and interference color.
However, simply using such image quality improving liquid may be insufficient to improve printed image quality in some cases. First, there is room for improvement in the image quality improving liquid itself. More specifically, although the amount of the water soluble resin contained in image quality improving liquid that remains at the surface of the print medium without permeating through does control bronzing and interference color, on the other hand, the amount of image quality improving liquid also affects the glossiness and image clarity of the image. Therefore, if the amount of image quality improving liquid remaining on the print medium surface could be controlled according to the properties of the image quality improving liquid itself, it would be possible to control not only bronzing and interference color, but also glossiness and image clarity. Second, the effects of using image quality improving liquid on a print medium may differ depending on whether an inkjet printing apparatus is executing a color mode or a monochrome mode, for example. For example, in the case of applying the image quality improving liquid to the print medium during the same scan as colored ink, more irregularities are formed on the surface of the print medium compared to the case of applying the image quality improving liquid after printing an image with colored ink, and these irregularities appear themselves as differences in glossiness, image clarity, and interference color. In addition, differences in the amount of image quality improving liquid used (the amount applied per unit area) appear themselves as differences in the above bronzing.